Do rare chance events shape evolution?

Historians can only speculate on what might have been, but a team of evolutionary biologists studying ancient proteins has turned speculation into experiment. They resurrected an ancient ancestor of an important human protein as it existed hundreds of millions of years ago and then used biochemical methods to generate and characterize a huge number of alternative histories that could have ensued from that ancient starting point.

Tracing these alternative evolutionary paths, the researchers discovered that the protein – the cellular receptor for the stress hormone cortisol – could not have evolved its modern-day function unless two extremely unlikely mutations happened to evolve first. These “permissive” mutations had no effect on the protein’s function, but without them the protein could not tolerate the later mutations that caused it to evolve its sensitivity to cortisol. In screening thousands of alternative histories, the researchers found no alternative permissive mutations that could have allowed the protein’s modern-day form to evolve. The researchers describe their findings June 16, online in Nature.

“This very important protein exists only because of a twist of fate,” said study senior author Joe Thornton, PhD, professor of ecology & evolution and human genetics at the University of Chicago. “If our results are general – and we think they probably are – then many of our body’s systems work as they do because of very unlikely chance events that happened in our deep evolutionary past,” he added.

This is a big debate in origin of life. Some say there is a law of nature that brings life about; others say it is chance. For a handy summary of the present stalemate, go to The Science Fictions series at your fingertips (origin of life)

5 Responses to Do rare chance events shape evolution?

Given all that we know about proteins and what life, even in its minimal form, requires, could it be said that Law Theorists for abiogenesis are sort of like medieval alchemists who thought that you could turn lead into gold, only without intentional intervention?

From Thornton’s Lab, More Strong Experimental Support for a Limit to Darwinian Evolution – Michael Behe – June 23, 2014
Excerpt: In prior comments on Thornton’s work I proposed something I dubbed a “Time-Symmetric Dollo’s Law” (TSDL).3, 8 Briefly that means, because natural selection hones a protein to its present job (not to some putative future or past function), it will be very difficult to change a protein’s current function to another one by random mutation plus natural selection.
But there was an unexamined factor that might have complicated Thornton’s work and called the TSDL into question. What if there were a great many potential neutral mutations that could have led to the second protein? The modern protein that occurs in land vertebrates has very particular neutral changes that allowed it to acquire its present function, but perhaps that was an historical accident. Perhaps any of a large number of evolutionary alterations could have done the same job, and the particular changes that occurred historically weren’t all that special.
That’s the question Thornton’s group examined in their current paper. Using clever experimental techniques they tested thousands of possible alternative mutations. The bottom line is that none of them could take the place of the actual, historical, neutral mutations. The paper’s conclusion is that, of the very large number of paths that random evolution could have taken, at best only extremely rare ones could lead to the functional modern protein.http://www.evolutionnews.org/2.....87061.html